The present invention relates to a process for the preparation of .beta.-aminoacrylic acid esters from acetic acid esters and aminal esters (alkoxybis-(dialkylamino)methanes).
A number of possible ways of preparing .beta.-aminoacrylic acid esters are known. An interesting industrial route is the reaction of amines with alkali metal salts of .beta.-hydroxy-acrylic acid esters, which are obtainable from CO, alcoholate and acetic acid esters in a pressure reaction requiring 20 to 50 bar. This route, known in principle from Annales de Chimie 18 (1932), 108, was improved to a total yield of about 70% in European Patent Specification 217 018. European Patent Specification 388 744 describes another variant with yields of 85 to 95% of the theoretical yield. In each of these cases, the reaction has to be carried out in high-pressure apparatuses; the high toxicity and the flammability of the CO requires special safety devices.
Highly toxic iron pentacarbonyl is used in the reaction of methyl acrylates with t-butoxy-bis-(dimethylamino)-methane (Tetrahedron Lett. 1976, 4061; An. Chem. 1980, 991). In addition, the polymerisation of the acrylic acid ester, which makes the reaction product more difficult to isolate, must be taken into account in this process.
The reaction of t-butoxy-bis-(dimethylamino)-methane with ethyl acetate (Chem. Ber. 104, 1971, 2709) gives 88% of .beta.-dimethylaminoacrylic acid ester after 20 hours at 170.degree. C. To achieve this, however, the process has to be carried out in a sealed tube and high pressures are attained at the end of the reaction due to the alcohol and dimethylamine produced. On further investigation of this reaction, it was found that when it is carried out in a 250 ml or 500 ml autoclave, only 60% of the theoretical yield is obtained (H. Saur, Thesis, Univ. Stuttgart 1971, p. 41). When a 50% excess of ethyl acetate is , used, .beta.-dimethylaminoacrylic acid ester is no longer formed, a higher-boiling substance being obtained instead. When methoxy-bis-(dimethylamino)-methane is reacted with ethyl butyrate, no reaction product is obtained at all (Org. Prep. Proceed. Int. 10, (1978), 67).